Electrochemical process for the extraction of copper and zinc from ores



H. S. MACKAY ELECTROCHEMICAL PROCESS FOR THE EXTRACT Nov. 26, 1929.

ION

OF' COPPER AND ZINC FROM ORES Filed Jan. 28, 1 926 awo@ *Ow SM sow 1 M .rJ fom @5x33 la raw k QdS 938mm #3HE Y SHOW QW SN zo @83am Q Patented Nov. 26, 1929 UNITED STATES PATENT OFFICE HENRY SQUAREBRIGS MACKAY, OF `LONDON,

ELECTROCHEMICAL PROCESS FOR THE EXTRACTION OF COPPER ZINC ORES Application led Ian'uary 28, 1926, Serial No. 84,377, and in Great Britain September 24, 1925.

In electro-chemical processes for-the extraction of copper from ores containing copper and zinc, the zinc in the ore goes into solution with the copper when the ore is leached with a solution of acid; Y Then when the solutions are treated by electrolysisthe copper is deposited and the zinc builds up in the solutions as the process proceeds.

Processes heretofore used for recovering zinc from such ores have been carried out by precipitating the copper and' other metals 25 from the solution and leaving the zinc in the solution, which-is afterwards treated either by `electrolysis or by other methods to recover the zinc.

According to my present invention, I propose to remove the zinc from the solution in the form of sulphate, which, if desired, may be dissolved and ele'ctrolyzed to produce metallic zinc'. I do this without removing all of the copper from solution. Thus, while 3.5 continuously producing electrolytic copper I prevent the zinc from building upto excess in the solution, and at the same time I recover the zinc. r i

In carrying out my present invention, the

40 orer is leached with a solutionfof sulphuric acid and the resultant solutions purified and electrciyzed in any suitable manner. After the solution h as been electrolyzedand zinc 1; accumulated therein to near the satura- ;Lrcint, ai or part ofthe solution is drawn off and passed through an evaporating plant. This evaporating plant is composed of pans or other apparatus of any suitable type for evaporating solutions. These pans comprising the evaporating plant may be advantageously heated by the furnace gases, produced from roasting the ore, or they may be; heated by any other suitable means.

From the electrolyzer, the solution containing a low percentage of `copper and a high 5 5 -percentage of zinc `is run into the evaporating plant. Here the solution is concentrated by evaporation and part of the zinc is crystallized out without affecting the bulk of the copper in the solution. For' example, if the 6o solution carries 1% copper-'and 8% zinc and its volume is 100 cubic meters, it is evaporated down to 5() cubic meters. During this process about half the zinc in the solution will have been crystallized out as-z'inc sul- 65 phate, with now andthen Aslight traces of copper, andthe percentage of copper will have'increasedto 2%. But since the copper Will not crystallize out in quantity until a much higher concentration is reached it is substantially not affected by the evaporation. By this principle of fractional crystallization part of the zinc can be lcontinuously taken out of the solution Without affecting `the copper, except for some relatively slight traces which are dealt withras hereinafter described. Any suitable processes may be used for ex; tracting the copper and zinc in solution from the ores. I .may employ. the vmethod illustrated in the accompanying ow sheet to whichI shall now refer.

-Ifnecessary, vtheraw ores are roasted to render copper and zin'c soluble. The ores,

concentrates orjresidues are delivered from the furnace A- by the conveyor B to the leach- Y S5 'in tanks F until a neutral or vnearly neutral metal-enriched solution is' obtained. This so- 9@ lution Which is of relatively high specific gravity is then delivered through line X into the agitator I, and the ore in tanks F is then leached with the stronger acid solution to extract the remaining metals.

This charge of ore, exhausted of its devsirable constituents is replaced in the tanks F by a fresh charge, and the acid solution last applied to 'the precedingcharge is used as the first leaching solution of the fresh charge.,

When this-solution has dissolved as much as possible of the metals it is passed o n to the agitator I through line X, and a fresh stronger acid solution is applied to this charge of ore, and so on with each successive charge.

The weaker acidsolution partly. metal bearing is in each case contained in the tank G and the stronger acid solution in the tank H.

In the agitator or purifying tower I the iron, aluminium and other impurities are precipitated to the required extent by any known or suitable methods of purification, (e. g. by the addition of calcium carbonate,) leaving in the solution vzinc as well as copper. The purified. solution is then passed to a filter press K from which the clear solution is drawn ofi' to a tank L.

The solution then .flows through the electrolytic cells M where a part of the copper is deposited, leaving the zinc in the' solution', which is then delivered through a lline 10 to an evaporating plant 11 heated by the products of combustion of the furnace A. lThe solution is heated and evaporated in plant l1 until saturation of the zinc content is reached, whereupon the hot solution is passed to crystallizing tanks 12 and allowed to cool until a part of the zine-sulphate is crystallized out. The residual solution from the tanks 12 may be returned either through line 13 to the evaporating plant 11 to join further quantities of solution from the electrolytic cells M, or it may be returned through line 14 to the tank L.

A line 15 is'provided to convey a part of the solution containing free sulphuric acid from the electrolytic cells M to the tanks L and H, to take care of cases in which quantities of the acid are required to standardize the solutions in either of the tanks.

The crystallized 'zinc sulphate formed inl the crystallizing tanks 12 usually containsl .traces `of copper. It is therefore passed through line 16 toa purifying tower 17, Where it is re-dissolved and treated with a suitable reagent, such as calcium carbonate or zinc dust, toprecipitate the copper. The

.clear solution thus obtained may thenbe de# canted directly to a tank 19' through line 17a,A or the solution and precipitate '1. ay be passed to a filter press 18 and thereseparated. 'lhe clear zine sulphate solution-is tl en passed to the storage tank 19, andjthe pr( cipitate (if calcium carbonate is used) retuined by line 20 to the purifying tower I,"Where the copper hydrate may be employed to percipitate iron and aluminum by recombing as sulphate. When zinc dust is used as the reagent in the purifying tower 17, the metallic copper precipitated in the reaction may be taken on a conveyor line 23 from the filterrpress 18to the furnace A, where the copper is remixed with the ore, concentrate or residue undergoing roasting.

A line 21 is provided'for the purpose of conveying the pure zinc sulphate solution to the evaporating plant 22 in which it is evaporated to obtain crystallized zinc sulphate. If desired, the clear zinc sulphate solution may be .electrolyzed to produce electrolytic zinc.

The present invention, therefore, provides a complete process f or the separate recovery of zinc and copper from ores containing both of these metals. The copper is deposited in the form of electrolyticcopper'without interference by the zinc during electrolysis, and the zinc is recovered in the formof pure zinc sulphate solution, which may either be evaporated to obtain crystallized zine sulphate or electrolyzed to produce electrolytic' zinc. The entire process is carried on in con-v tinuous cycle without the mutual interference of the zinc and the copper.

With reference to the accompanying flow sheet I have described a complete process in accordance with my present invention sufricient to enable the same to be carried into practice by those skilled in the art.

As regards the methods of roasting, leaching and purifying, a detailed descriptionv of highly advantageous methods will be lfound in the specification of my United States PatentNo. 1,598,296.

What I claim isz- 1. A processfor recovering copper and zincfrom ores or metallurgical products consisting in obtaining the copperand zinc in solution as sulphates, electrolyzing the solution, depositing a portion oflthe copper until the concentration of copper sulphate is low, relatively to thezinc sulphate in the solution, evaporating such solution to crystallze outa portion of the zinc sulphate, redissolving the zinc sulphate crystals and treating the resulting solution with a reagent to precipitate as hydrates such copper or other imY purities as may have been crystallized witl the zinc, and employing the precipitated copper hydrate in the purification of the zinc and copper sulphate solution before electrolysis.

2. A process for recovering copper and zinc from ores or metallurgical products consist-A ing in obtaining the copper and zinc in solution as sulphates, electrolyzing the solution, depositing-a portion of the copper until the concentration of copper sulphate is low relatively to the zinc sulphate in the solution, evaporating suchsolution to crystallize out a portion of the zinc sulphate, redissolving the zinc. sulphate crystals and treating the resnlting solution with a reagent to precipitate ras hydrates such copper or other impurities HENRY SQUAREBRIGS MACKAY. 

